Liquid and vapor flow in superheated rock

In this review, we describe the dynamics and thermodynamics of liquid and v apor flow through hot fractured rock. Such flows occur in geothermal reserv oirs and have important implications for geothermal power generation; we de scribe both forced flows associated with liquid injection into such systems , and natural convective Bows associated with the vertical heat transfer th rough such systems. First we focus on permeable media and describe the heat transfer of single-phase liquid or vapor flow through a medium of differen t temperature. Then we consider the dynamics and thermodynamics of a liquid front as it advances into a superheated region and boils. The morphologica l stability of such an interface is discussed, and we describe conditions u nder which the interface breaks down to form a two-phase zone between the l iquid and vapor. We next examine the heat transfer and boiling in gravity-d riven hows advancing through a superheated permeable rock, identifying that at large times such currents asymptote to a family of similarity solutions . In the second part of the review, we describe the analogous heat transfer and boiling processes associated with liquid flow along a fracture embedde d in an impermeable rock. We describe some simple asymptotic solutions for the temperature distribution in the bounding rock, which reveal that in the fracture, a two-phase boiling region develops between the purely liquid an d purely vapor zones. Model predictions are successfully tested with labora tory experiments. In the final section of the review, we briefly discuss na tural convective flows, illustrating how single-phase and two-phase convect ive regions interact and in some cases produce instability.